North Equatorial Current (NEC) bifurcation
報告人:沈茂霖 (Mao-Lin Shen)
112/04/21
Seminar report
112/04/21 Mao-Lin Shen, Dept. of Atmospheric Sciences, NTUMao-Lin Shen, Dept. of Atmospheric Sciences, NTU Page 2
Thermohaline Circulation
112/04/21 Mao-Lin Shen, Dept. of Atmospheric Sciences, NTUMao-Lin Shen, Dept. of Atmospheric Sciences, NTU Page 3
The Great Indo-Pacific Communicator
Fig. The Great Indo-Pacific Communicator. (by Oppo and Rosenthal, 2010, Science)
112/04/21 Mao-Lin Shen, Dept. of Atmospheric Sciences, NTUMao-Lin Shen, Dept. of Atmospheric Sciences, NTU Page 4
NECt-Mindanao Current-Kuroshio (NMK) system
Fig. Schematic chart of geostrophic volume transport relative to 1200 dbar-depth in the North Equatorial Current-Mindanao Current-Kuroshio (NMK) system. (by Nitani, 1972)
112/04/21 Mao-Lin Shen, Dept. of Atmospheric Sciences, NTUMao-Lin Shen, Dept. of Atmospheric Sciences, NTU Page 5
Cruise measure
Fig. NEC bifurcation near the Philippine Coast. NEC flow poleward of this latitude turned north as the Kuroshio while flow to the south fed the Mindanao Current. (by Toole et al., 1990, JPO)
112/04/21 Mao-Lin Shen, Dept. of Atmospheric Sciences, NTUMao-Lin Shen, Dept. of Atmospheric Sciences, NTU Page 6
Cruise measure
Fig. NEC bifurcation near the Philippine Coast in different cruise measures.
(b) 23 April 1988(a) 20 Sep 1987
112/04/21 Mao-Lin Shen, Dept. of Atmospheric Sciences, NTUMao-Lin Shen, Dept. of Atmospheric Sciences, NTU Page 7
Fig. Time series of the NEC bifurcation latitude anomalies (solid line) versus the southern oscillation index (SOI) (dashed line). A 12-month running mean filter was applied. (by Qiu and Lukas, 1996, JGR)
112/04/21 Mao-Lin Shen, Dept. of Atmospheric Sciences, NTUMao-Lin Shen, Dept. of Atmospheric Sciences, NTU Page 8
NEC bifurcation point moves southward in summer and northward in winter.
The bifurcation is depth dependent. The northernmost Bifurcation point is at warm ENSO
phase (El Niño) and the southernmost at cold ENSO phase (La Niña).
The seasonal bifurcation and inter-annual bifurcation are due to different mechanisms.
112/04/21 Mao-Lin Shen, Dept. of Atmospheric Sciences, NTUMao-Lin Shen, Dept. of Atmospheric Sciences, NTU Page 9
Streamfunction
Fig. Comparison different methods applied for determining streamfunction.
(b) Winter(a) Summer
112/04/21 Mao-Lin Shen, Dept. of Atmospheric Sciences, NTUMao-Lin Shen, Dept. of Atmospheric Sciences, NTU Page 10
112/04/21 Mao-Lin Shen, Dept. of Atmospheric Sciences, NTUMao-Lin Shen, Dept. of Atmospheric Sciences, NTU Page 11
Summer and winter (1)
Fig. Comparison of stream function on summer and winter.
(b) Winter(a) Summer
112/04/21 Mao-Lin Shen, Dept. of Atmospheric Sciences, NTUMao-Lin Shen, Dept. of Atmospheric Sciences, NTU Page 12
Summer and winter (2)(b) Winter(a) Summer
Fig. Comparison of stream function on summer and winter.
112/04/21 Mao-Lin Shen, Dept. of Atmospheric Sciences, NTUMao-Lin Shen, Dept. of Atmospheric Sciences, NTU Page 13
Depth dependence
Fig. Stream function comparison of the flow rate integrated from different depths.
(b) 0-400 m averaged.(a) 0-800 m averaged.
112/04/21 Mao-Lin Shen, Dept. of Atmospheric Sciences, NTUMao-Lin Shen, Dept. of Atmospheric Sciences, NTU Page 14
Depth dependence
Fig. Stream function comparison of the flow rate integrated from different depths. An interesting phenomenon is the deep circulation in the SCS is stronger than surface circulation.
(b) 400-800 m averaged.(a) 0-400 m averaged.
112/04/21 Mao-Lin Shen, Dept. of Atmospheric Sciences, NTUMao-Lin Shen, Dept. of Atmospheric Sciences, NTU Page 15
Annual variation of LST
50 100 150 200 250 300 350
500
1000
1500
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Day
Dep
th (
m)
-4
-2
0
2
4
50 100 150 200 250 300 350
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2000
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Dep
th (
m)
-4
-2
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Fig. Annual variation of Luzon Strait Throughflow.
112/04/21 Mao-Lin Shen, Dept. of Atmospheric Sciences, NTUMao-Lin Shen, Dept. of Atmospheric Sciences, NTU Page 16
Impact of different sill depth
Fig. Comparison of different sill depth.
(b) Shallower Bathymetry(a) Realistic Bathymetry
112/04/21 Mao-Lin Shen, Dept. of Atmospheric Sciences, NTUMao-Lin Shen, Dept. of Atmospheric Sciences, NTU Page 17
Impact of different sill depth(b) Shallower Bathymetry(a) Realistic Bathymetry
Fig. Comparison of different sill depth.
112/04/21 Mao-Lin Shen, Dept. of Atmospheric Sciences, NTUMao-Lin Shen, Dept. of Atmospheric Sciences, NTU Page 18
Impact of different sill depth
50 100 150 200 250 300 350
100
200
300
400
500
Day
Dep
th (
m)
-4
-2
0
2
4
50 100 150 200 250 300 350
100
200
300
400
500
Day
Dep
th (
m)
-4
-2
0
2
4
Fig. Comparison of different sill depth. Top panel: RB; bottom panel: SB.
112/04/21 Mao-Lin Shen, Dept. of Atmospheric Sciences, NTUMao-Lin Shen, Dept. of Atmospheric Sciences, NTU Page 19
The impact of southern throughflow
Fig. Comparison of stream function on different southern throughflow.
(b) 8 Sv(a) 0 Sv
112/04/21 Mao-Lin Shen, Dept. of Atmospheric Sciences, NTUMao-Lin Shen, Dept. of Atmospheric Sciences, NTU Page 20
The bifurcation may be due to upstream flow rate and the local topography as well as the surrounding current system.
Depth dependent bifurcation may have seasonal variation and the mechanism shall be found.
Does the bifurcation have connection with the SSHa attributed by ENSO events?? How could we verify this by our model??
The seasonal bifurcation is determined by the LST.
112/04/21 Mao-Lin Shen, Dept. of Atmospheric Sciences, NTUMao-Lin Shen, Dept. of Atmospheric Sciences, NTU Page 21
Thank you for your attention.